This invention relates to the manufacture of threaded fasteners and, more particularly, to the dies for roll forming threads on the male fastener element, to associated method and to the resultant threaded article.
Threaded fasteners are widely used to connect separate components and are employed in myriad applications. Such fasteners typically include a threaded male member comprising a cylindrical body or shank with a roll formed thread on its exterior. An example of a fastener with roll formed threads is disclosed in U.S. Pat. No. 7,326,014 entitled “Interactive Fit Screw Thread.”
A common method for manufacture of male threaded fastener elements is to employ roll form dies to create the threads on the cylindrical body or blank. Multiple revolutions of the blank are employed to progressively deform the blank material to fully form the thread crests and roots. Thus, with each revolution of the blank, partial metal deformation occurs. Generally the greater the thread depth, the more revolutions of the blank are required to complete the final thread form.
In a standard thread roll die, multiple straight, angled lines are provided to enable the formation of a helical thread. Two dies are provided, one that is stationary and one that moves linearly with respect to the non-moving die. The movement of the moveable die with respect to the stationary die causes the screw blank to rotate and advance along the die surfaces. As the blank rotates, the threads begin to form.
Existing flat thread rolling tooling available is manufactured with the thread form following a straight line. All current manufacturing processes are built around cutting and grinding shapes into tooling based on straight lines.
It is generally desirable for the blank to be realigned with the dies upon each rotation. This means that, at the start of the forming process, the blank is located in a certain position with respect to the thread rolling forms (lines) and upon each complete rotation, is positioned in the same position (albeit offset from the original starting point) with respect to the thread forms. In this way, as the helical thread is formed, the thread will be uniform without deformations being formed thereon. Also, if the thread forms are aligned upon each rotation, less wear and damage will occur to the thread forms.
During the manufacture of some fasteners, it was noted that deformations were being created on the threads. The deformations are not insignificant given the importance of, for example, the wavy thread form of the fastener shown in U.S. Pat. No. 7,326.014.